Au Grating Research Articles

Electrically detectable surface plasmon resonance sensor by combining a gold grating and a silicon photodiode

We propose an electrically detectable surface plasmon resonance sensor in a liquid consisting of a Au grating and a silicon p+n photodiode. The surface plasmon resonance (SPR) was excited on the Au grating, affecting the photovoltaic signal of the photodiode under the grating. The SPR signal was thus measured by obtaining the electrical signal without reflection measurements and a polarizer. The SPR conditions were clearly measured with our proposed sensor. It was verified that the SPR condition could also be measured without polarizing the incident light. The dielectric constant of water was determined using the proposed sensor.

ワンチップSPRセンサのための回析格子型Si近赤外検出器

We propose a one-chip Surface Plasmon (SPR) sensor by using a near infrared photodetector (NIR-PD), which consists of Au grating on a silicon substrate. Since SPR is usually measured by reflection intensity, a large space for measuring the intensity is required. Thus, we propose the SPR sensor, which can detect an SPR condition without measuring the reflection intensity. A dielectric constant of the material on the Au grating can be obtained by observing the change of an SPR condition, which is measured by the short circuit current of the NIR-PD. In this paper, we show that an SPR condition can be measured by using the NIR-PD. In addition, from results of an optical simulation, we show that an SPR condition can be changed due to the dielectric constant of the surface of an Au grating. These results imply that our proposed one-chip SPR sensor can be realized.

Excitation of surface phonon polariton modes in gold gratings with silicon carbide substrate and their potential sensing applications

We demonstrate the excitation of surface phonon polaritons (SPhPs) in the mid-infrared (mid-IR) Reststrahlen band (10.288μm-12.563μm) on patterned surfaces with silicon carbide (SiC) substrate and gold (Au) gratings. The very large negative permittivity of Au limits its applications in the mid-IR range, and to couple incident light to SPhPs modes, their momentum mismatch can be compensated by patterning Au grating onto the surface of SiC substrate. Samples were fabricated and characterized experimentally by Fourier transform infrared reflection (FTIR) spectroscopy. The optical properties were also simulated by the rigorous coupled wave analysis (RCWA) method. Reflection dips are observed for light polarized vertical to the grating lines (TM-polarized), which are attributed to the coupling of electromagnetic (EM) waves into the SPhP modes. In addition, we present small-volume index sensing with analyte specificity based on mid-IR SPhPs in the fabricated configuration.

NIR spectrometer using a Schottky photodetector enhanced by grating-based SPR.

We present a near-infrared (NIR) spectrum measurement method using a Schottky photodetector enhanced by surface plasmon resonance (SPR). An Au grating was fabricated on an n-type silicon wafer to form a Schottky barrier and act as an SPR coupler. The resulting photodetector provides wavelength-selective photodetection depending on the SPR coupling angle. A matrix was pre-calculated to describe this characteristic. The spectrum was obtained from this matrix and the measured photocurrents at various SPR coupling angles. Light with single and multiple wavelengths was tested. Comparative measurements showed that our method is able to detect spectra with a wavelength resolution comparable to that of a commercial spectrometer.

Electromagnetic resonance modes on a two-dimensional tandem grating and its application for broadband absorption in the visible spectrum.

In this work, we numerically investigate the electromagnetic resonances on two-dimensional tandem grating structures. The base of a tandem grating consists of an opaque Au substrate, a SiO(2) spacer, and a Au grating (concave type); that is, a well-known fishnet structure forming Au/SiO(2)/Au stack. A convex-type Au grating (i.e., topmost grating) is then attached on top of the base fishnet structure with or without additional SiO(2) spacer, resulting in two types of tandem grating structures. In order to calculate the spectral reflectance and local magnetic field distribution, the finite-difference time-domain method is employed. When the topmost Au grating is directly added onto the base fishnet structure, the surface plasmon and magnetic polariton in the base structure are branched out due to the geometric asymmetry with respect to the SiO(2) spacer. If additional SiO(2) spacer is added between the topmost Au grating and the base fishnet structure, new magnetic resonance modes appear due to coupling between two vertically aligned Au/SiO(2)/Au stacks. With the understanding of multiple electromagnetic resonance modes on the proposed tandem grating structures, we successfully design a broadband absorber made of Au and SiO(2) in the visible spectrum.

Antireflection Coatings on Au Plasmonic Gratings for Infrared Photodetection

Based on analytic formulas and numerical simulations, we investigate the enhancement effect of dielectric antireflection coatings on the performance of quantum-well infrared photodetectors (QWIP) with Au grating couplers and operating at 15 μm. It is found that a simple analytic formula can well estimate the optimal coating thickness. By using a GaAs-coated Au grating with optimal parameters, the absorption can be enhanced by 13 times in the QW active region compared with the reference structure (without Au grating and with an isotropic active region). This enhancement is about three times of that without a dielectric coating. For s-polarized light, a high enhancement (>5) can occur in a broad range of incident angle (|𝜃|<60∘).

Effects of relief gratings, light characteristics and material properties to the emission resonance region

We present numerical simulations in order to investigate the coupling of the incident radiation to Surface Plasmon polaritons (SPPs) by metallic relief gratings. When the frequency of the SPPs is coincident with the electromagnetic waves, there is a strong absorption of the electromagnetic waves. This phenomenon is called surface Plasmon resonance (SPR). The effects of surface materials, characteristics of incident light and the geometrical shapes on the SPR are studied by using the rigorous coupled-wave algorithm (RCWA). The results reveal that a peak of high emissivity is obtained for Au compared with W, Cu and Al. This explained that the gold is the best transition metal used for the excitation of SPPs. At the resonance the absorption of light by the (Au) grating is greater for grazing than normal incident light. Every considered transition material has the particular wavelength emission region and the period emission region. The influence of gratings geometric parameters on the SPR is also presented.   Â

Design of Plasmonic Perfect Absorbers for Quantum-well Infrared Photodetection

Based on analytic formulas and numerical simu- lations, we propose a plasmonic cavity with a top Au grating and bottom Au film to enhance quantum-well infrared pho- todetectors (QWIPs) operating at wavelengths between 2 and 30 μm. By using plasmonic cavity modes, QWIPs can detect light even at normal incidence. With using optimal structural parameters, light can be almost perfectly absorbed by the cavity and over 54 % of the light is absorbed by the QW active region. Compared with the reference structure (without Au layers and with an isotropic active region), the absorption enhancement is over 30 times in the QW active region at normal incidence and remains high value (> 4.5) for p -polarized light in a broad range of incident angle (|θ| < 60 0 ).

Multiple plasmonic effect on photocurrent generation of metal‐loaded titanium dioxide composite/dye films on gold grating surface

We demonstrate the multiple plasmonic effect on the photocurrent properties of photoanodes containing Ag or Au nanoparticles (NPs) loaded onto titanium dioxide film (Ag–TiO2 or Au–TiO2) on Au grating surfaces. Ag–TiO2 or Au–TiO2 nanocomposite particles are prepared by a flame spray pyrolysis route. The structures and morphologies of the prepared products are characterized by high‐resolution transmission electron microscopy. The Ag–TiO2 or Au–TiO2 composite NPs are deposited by spin coating onto the Au grating surfaces. The photoanode electrode is a layered structure of blu‐ray disc‐recordable grating substrate/Au/Ag (or Au)–TiO2/dye/electrolyte/indium‐tin oxide. The plasmonic effect is induced when Ag or Au NPs are located within the propagating surface plasmon (SP) field on the Au grating surface. The short‐circuit photocurrent is increased by exciting the grating‐coupled propagating SP on the Au gratings and is further enhanced by positioning the Ag or Au NPs within the grating‐coupled SP field. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Surface-enhanced fluorescence of a dye-doped polymer layer with plasmonic band edge tuning

We investigated experimentally the influence of 1D rectangular Au gratings on fluorescence. The formation of a bandgap in the dispersion relation is confirmed by our experiment. At the edge of this bandgap, the fluorescence of the dye can be strongly enhanced due to the surface plasmon polaritons' large density of states. By structural design we tuned the plasmonic band edges to the wavelength of the fluorescence of the dye molecules. An optimized Au grating structure with a duty ratio of 3/4 is found to achieve up to 120 times stronger fluorescence than that of a planar metal surface.

Design principle of Au grating couplers for quantum-well infrared photodetectors

Based on analytic formulas and numerical simulations, we investigate the enhancement effect of Au gratings with spoof plasmon resonances on quantum-well infrared photodetectors (QWIPs) operating between 2 and 30μm. It is found that a simple analytic formula can well estimate the resonant wavelengths of Au gratings. Using optimal grating parameters, the absorption in the QW active region can be enhanced by 4-5 times compared with that in the reference structure (without gratings and with an isotropic active region). For s-polarized light, a high enhancement (>1.4) can occur in a broad range of incident angle (|θ|<40°).

Thermo-optic modulation of plasmonic bandgap on metallic photonic crystal slab

We demonstrate active control of plasmonic bandgap on a metallic photonic crystal slab using thermo-optic effects. The Au grating, which is milled by focused-ion beam on a glass substrate, is designed to exhibit an extraordinary optical transmission and a sharp transitional edge for high modulation efficiency. Only a moderate refractive index modulation of Δn = 0.0043 is required to obtain more than 60% modulation depth with surface-normal optical coupling.

STATEMENT OF RETRACTION: "MEASUREMENT OF THE CASIMIR INTERACTION BETWEEN A Au SPHERE AND Au GRATINGS"

This article was published as a part of the conference proceedings for the Eighth Alexander Friedmann International Seminar on Gravitation and Cosmology and Satellite Symposium on the Casimir Effect, held in Rio de Janeiro, Brazil, 30 May–3 June 2011. In the article I described results of the force obtained in the Casimir regime between a Au coated sphere and a Au grating. The making of the grating required extensive development from my collaborators. The article was published without the proper authorship from the research groups involved. Against this background I thus retract my article and apologize for the damage I have caused.

Tunable gold-coated polymer gratings for surface plasmon resonance coupling and scanning

We propose an surface plasmon resonance (SPR) coupling device that can tune the coupling condition by changing the pitch of an Au grating. A grating with a micrometer-sized pitch was produced on a flexible thin parylene membrane, making an 8 mm × 8 mm diaphragm. An SPR can be coupled to the Au grating surface by direct laser irradiation, and the dependence of the SPR angles (within 6° to 56°) on the grating pitch (ranging from 1000 to 1500 nm) shows good agreement with the SPR theory. We demonstrate that the SPR matching condition can be tuned by changes in pitch due to strain caused by membrane expansion. The SPR angle shift reached about 0.2°, corresponding to about 0.6% strain, by 15 kPa pressure application. The SPR angle shift sensitivity to the pressure was 0.015° kPa−1. This value is almost equal to that calculated from strain measurements (0.014° kPa−1), and we conclude that the SPR angle shift was caused by the grating pitch change due to the pressure application. Theoretical consideration indicates that a refractive index change of about 0.01 RIU is possible with this device near the refractive index of water.

Design of midinfrared photodetectors enhanced by resonant cavities with subwavelength metallic gratings

We propose a metallic Fabry–Pérot cavity with a Au grating and a Au film acting as two reflectors to enhance the field and absorption in the active detector region, leading to better performance of quantum-dot-based photodetectors at a wavelength of 10 μm. One- and two-dimensional Au gratings are applied to achieve enhancement for polarized and unpolarized light, respectively. With optimizing grating parameters, the absorption can be enhanced by about 20 times in the active detector region compared to conventional photodetectors without the Au reflectors.

Resonator combined with a piezoelectric actuator for chemical analysis by force microscopy

A high frequency silicon resonator for dynamic scanning force microscopy is combined with an integrated piezoelectric actuation element for large displacements. A high resonance frequency is required for imaging on the nanometer scale, and a large displacement is needed for the chemical analysis of the material at the end of the probe. The small piezoelectric resonator is formed at the end of a long piezoelectric actuator using a silicon micromachining technology. The resonator can be oscillated at 96.4 kHz, and the actuator generates a maximum displacement of 15 microm at the end of the probe. The dynamic-mode scanning force microscopy capability, using the integrated piezoelectric resonator, is demonstrated on a 2 microm pitch Au grating.

Polarization properties of subwavelength metallic gratings in visible light band

Optical polarization properties of aluminum, gold and aluminum/gold subwavelength metallic gratings (SWMGs) are investigated numerically in the visible light band. Their performance as polarizing beam splitters are simulated with RCWA for varied metallic materials, grating depth and incident angle. Metallic waveguide theory is applied to explain the performance difference between Au and Al grating. A new type of Al/Au bimetallic is also investigated numerically for potential applications.